The present invention relates generally to disaster recovery for online computer systems. More particularly, the present invention relates to the creation of a standby data processing site at a remote location using reduced communication bandwidth mirroring.
In recent years, the use of networked computer software and the Internet has brought about a significant increase in the amount of network traffic and transactions performed by software applications residing on remote servers. More information is stored by these networked applications and in remote database applications than ever before. These applications process a large number of purchase transactions, credit card transactions, electronic mailing lists, email functions, data distribution, batch processing, etc. These systems contain very critical data and it must be backed up so that the information is not lost. Further, application end users also desire that networked applications and data should be available 24 hours a day and 7 days a week.
To provide robust services that are constantly available, computer systems must have redundant backup systems. It is inevitable that the primary system will fail on occasion. When the primary system fails, a backup system must be quickly available. A backup system can be located on-site with the primary system and then a secondary backup system can be located at a physically remote backup site. Having at least one backup system on-site is valuable because the networked application can immediately failover to that application, if the primary system becomes inoperative. This fast failover will be transparent to the user because it is local.
A second backup system at a remote site is desirable because it protects against catastrophic failure at the primary site. This is sometimes called the standby site. If the primary site is disabled by an extended power outage, fire, or flood then the remote standby system will be activated. A failover to an off-site standby system is slower, but it provides a maximum amount of protection against total system failure. Specifically, this type of fail safe system is valuable for applications that are connected to the Internet which need to be constantly available.
Many online, transaction based systems store more than one copy of their data. This is another safeguard against system failure or data corruption. The first copy is an original copy and the second is an archival copy. The archival copy is a backup but other times it is used for error checking purposes. Some systems can even store multiple backup copies.
For certain transactional systems, such as a database, an active transaction log is kept which tracks recent transactions. An archive log is then kept to store information from the active log after the active log has been filled or a certain time period has passed. To be able to mirror a transactional system between the primary site and the standby site both the active logs and then the archive logs must be transferred to the standby system. The active logs are then entered into or applied to the standby system which constantly keeps the standby system current.
In the event of a failure, the standby system is always ready to take over. Usually, the standby system is located in another building or in a geographically remote area. This requires the active logs, archive logs, or backups to be transferred across a wide area network (WAN), which is relatively slow in comparison to a local area network (LAN) or a high speed cluster connection. As a result, the data sent from the primary site across the WAN to the standby site can cause a significant amount of network congestion. Especially where these files can contain hundreds of megabytes of data per file.
This invention provides a method for creating a standby data processing system located at a standby site, which is remotely located from a primary site. The method comprises a first step of computing a difference between an active data file and an archive data file to produce a delta image at the primary site. A second step is transmitting the active data file and the delta image, separately in time sequence, from the primary site to the standby site. A final step is combining the delta image with the active data file at the standby site, to produce a standby archive data file.
In accordance with one aspect of the present invention, the system includes a method for creating archive redo logs for a standby database at a remote location. The method includes the first step of trapping file system transactions using a primary archive log replicator to create an online redo log at the standby database. The next step is computing a difference between an online redo log and archive redo log in the primary database to create a delta image. Then the delta image is transmitted to a standby archive log replicator contained in the standby database.
Another step is combining the delta image with the online redo log in the standby database to create a standby archive redo log on the standby database. The final step is applying the updated archive redo log to the standby database.
Additional features and advantages of the invention will be set forth in the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate by way of example, the features of the invention.